The present invention relates to a method for regenerating a diesel particulate filter in the exhaust gas system of a diesel engine and for controlling a diesel engine which is set up for carrying out the method.
Diesel particulate filters (DPFs) in the exhaust gas system of diesel engines are used to remove unburned soot particles from the exhaust gas. Filters such as these are regenerated periodically by burning the accumulated particulate matter. The particulate matter ignites only at relatively high temperatures, typically, about 550xc2x0 C. Temperatures such as these are reached only in high load and high engine speed conditions. To ensure operation of the DPF, measures are taken to increase the exhaust gas temperature to sufficiently high levels, regardless of engine operating condition, to cause DPF regeneration.
DE 34 08 057 describes a method to ignite particulate matter in a DPF of a diesel engine by increasing the engine load using vehicle brakes, compression release brakes, exhaust brakes, or the like. This applies mainly to commercial vehicles.
DE 43 21 767 is of similar content as DE 34 08 057, but directed to industrial vehicles.
DE 39 09 932 describes a method to regenerate a DPF for an engine with a turbocharger where for low to medium engine loads the exhaust gas will bypass the turbocharger to increase the exhaust temperature and at the same time reduce the intake airflow or use an intake airflow heater.
DE 42 34 841 describes a method to regenerate a DPF for diesel engines by adjusting EGR. To increase the exhaust temperature, EGR rate is reduced.
DE 31 25 305 describes a method to regenerate a DPF for an engine with a turbocharger. A controlled portion of the exhaust gas stream bypasses the turbocharger.
Other procedures have been proposed for such an increase in the exhaust gas temperature. For example, engine load can be increased artificially by switching on electrical loads. If the diesel engine is equipped with a catalytic converter upstream of the DPF additional fuel can be injected into the combustion chamber or into the exhaust gas system. The unburned fuel is oxidized in the catalytic converter causing heat release and a temperature rise in the DPF.
The inventors of the present invention have recognized that individual measures such as these result in problems in that they intervene in complex mutual relationships so that, depending on the engine operating conditions; even the opposite of the desired effect can occur in some circumstances. To illustrate the problem, limits and interactions between the various subsystems for exhaust gas temperature control are described, by way of example, in the following text:
i. Exhaust gas temperature may be as low as 100xc2x0 C. when the engine is idling, operating at low load, or operating at low speed. This temperature is well below the lightoff temperature or activation temperature of the catalytic converter, that is, below the temperature at which significant oxidation rates are achieved for hydrocarbons and carbon monoxide. Thus, in operating conditions such as these, post injection of fuel, with the aim of passing hydrocarbons to the oxidation catalytic converter, would have negligible effect on the inlet temperature at the DPF.
ii. At higher engine speeds and loads, exhaust gas temperature is high enough for the catalytic converter to cause oxidation of hydrocarbons, carbon monoxide and unburned fuel. However, the speed of the gases through the converter may be too high, so that the residence time in the catalytic converter is insufficient for complete conversion of the unburned hydrocarbons.
iii. By restricting intake flow, the ratio between the pressure in the exhaust manifold and in the intake manifold rises. This pressure ratio causes exhaust gas recirculation (EGR) flow when the EGR valve is open. If the intake is restricted to a major extent by closing the intake throttle valve, EGR can become excessive.
iv. Reducing intake throttle opening increases engine pumping losses, which leads to a reduction in the torque available at the shaft.
v. If engine load is high, i.e., the main fuel injection quantity is high, and the intake is restricted, the air/fuel ratio may become too low meaning that there is little oxygen remaining after the combustion event. Post-injected fuel cannot be oxidized in the catalytic converter and oxygen is not available for combustion of the carbon in the DPF.
vi. The turbocharger, if the engine is so equipped, may have a variable geometry turbine (VGT) in the exhaust duct which is coupled by a shaft to the intake compressor in the intake duct. VGT provides a degree of control over intake pressure by adjusting the angle of the turbine""s vanes. If the turbocharger has a VGT, the turbine vanes are closed when the throttle valve is closed. This can lead to turbocharger over speed and an unnecessary temperature drop across the turbine.
A method for raising the temperature in a particulate filter, which overcomes disadvantages of prior approaches, is disclosed. The particulate filter is located in an exhaust duct coupled to a multi-cylinder, reciprocating engine located downstream of a catalytic converter which is also located in the exhaust duct. The method includes the steps of: closing, at least partially, an exhaust gas recirculation valve; adjusting an intake throttle valve disposed in the intake duct toward a closed position to provide a desired intake pressure; and increasing a main quantity of fuel supplied in a main fuel injection in response to the above steps. Preferably, the method further includes: discontinuing feedback control of a variable geometry turbine located in the exhaust duct upstream of the catalytic converter in response to closing the exhaust gas recirculation valve; injecting a quantity of post injected fuel when a temperature in a catalytic converter exceeds a predetermined activation temperature; and adjusting a timing and quantity of a pilot injection such that a noise level generated by combustion in the engine remains below a predetermined acceptable level.
A system for an engine capable of increasing temperature in a particulate filter disposed in an exhaust coupled to the engine is disclosed. The engine has a multiplicity of cylinders with pistons reciprocating within the cylinders, an intake with an intake throttle valve, a fuel injection system providing at least one fuel injector in each cylinder, and an exhaust gas recirculation system. The engine has an exhaust turbine located upstream of the particulate filter in the exhaust. The exhaust gas recirculation system is coupled to the engine intake and the engine exhaust via an exhaust gas recirculation valve. The fuel injection system is capable of providing multiple injections in each cylinder during a single revolution of the engine. The system includes an electronic control unit operably connected to the engine, the exhaust recirculation valve, the throttle valve, and the fuel injectors. The electronic control unit closes, at least partially, the exhaust gas recirculation valve; closes, at least partially, the intake throttle valve; increases a quantity of main fuel supplied in a main fuel injection event.
An advantage of the present invention is that a coordinated method for regeneration of the particulate filter in a diesel engine is provided. The method takes into account of the relationships between the various parameters and ensures a robust regeneration under all engine operating conditions. Furthermore, the coordinated approached of the present invention overcomes the difficulty with prior approaches in that they occasionally cause the opposite of the desired effect.